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Experimental Dyeing And Comparative Dye Testing

Every dyer ought to be able to make experiments in the mordanting and
dyeing of textile fibres for the purpose of ascertaining the best
methods of applying mordants or dye-stuffs, the best methods of
obtaining any desired shade, and for the purpose of making comparative
tests of dyes or mordanting materials with the object of determining
their strength and value. This is not by any means difficult, nor does
it involve the use of any expensive apparatus, so that a dyer need not
hesitate to set up a small dyeing laboratory for fear of the expense
which it might entail.

In order to carry out the work indicated above there will be required
several pieces of apparatus. First a small chemical balance; one that
will carry 50 grammes in each pan is quite large enough, and such a
one, quite accurate enough for this work, can be bought for 25s. to
30s., while if the dyer be too poor even for this a cheap pair of
apothecaries' scales might be used. It is advisable to procure a set
of gramme weights and to get accustomed to them, which is not by any
means difficult.

In using the balance always put the substance to be weighed on the
left-hand pan and the weights on the right-hand pan. Never put
chemicals of any kind direct on the pan, but weigh them in a
watch-glass, small porcelain basin, or glass beaker (which has first
been weighed), according to the nature of the material which is being
weighed. The sets of weights are always fitted into a block or (p. 212)
box, and every time they are used they should be put back into their
proper place.

The experimenter will find it convenient to provide himself with a few
small porcelain basins, glass beakers, cubic centimetre measures, two
or three 200 c.c. flasks with a mark on the neck, a few pipettes of
various sizes, 10 c.c., 20 c.c., 25 c.c.

The most important feature is the dyeing apparatus. Where only a
single dye test is to be made a small copper or enamelled iron
saucepan, such as can be bought at any ironmongers may be used; this
may conveniently be heated by a gas-boiling burner, such as can also
be bought at an ironmongers or plumbers for 2s.

It is, however, advisable to have means whereby several dyeing
experiments can be made at one time and under precisely the same
conditions, and this cannot be done by using the simple means noted

To be able to make perfectly comparative dyeing experiments it is best
to use porcelain dye-pots (these may be bought from most dealers in
chemical apparatus), and to heat these in a water-bath arrangement.

The simplest arrangement is sketched in figure 33; it consists of a
copper bath measuring 15 inches long by 10-1/2 inches broad and (p. 213)
6-1/2 inches deep; this is covered by a lid on which are six apertures
to take the porcelain dye-baths. The bath is heated by two round
gas-boiling burners of the type already referred to.

The copper bath is filled with water which, on being heated to the
boil by the gas burners, heat up the dye-liquors in the dye-pots. The
temperature in the dye-pots under such conditions can never reach the
boiling point; where it is desirable, as in some cases of wool
mordanting and dyeing that it should be so high, then there should be
added to the water in the copper bath a quantity of calcium chloride,
which forms a solution that has a much higher boiling point than that
of water, and so the dye-liquors in the dye-pots may be heated up to
the boil.

An objection might be raised that with such an apparatus the
temperature in every part of the bath may not be uniform, and so the
temperature of the dye-liquors in the pots might vary also, and
differences of temperature often have a considerable influence on the
shade of the colour which is being dyed. This is a minor objection,
which is more academic in its origin than of practical importance. To
obviate it Mr. William Marshall, of the Rochdale Technical School, has
devised a circular form of dye-bath, in which the temperature in every
part can be kept quite uniform.

The dyeing laboratories of Technical Schools and Colleges are
generally provided with a more elaborate set of dyeing appliances.
These in the latest constructed consist of a copper bath supported on
a hollow pair of trunnions, so that it can be turned over if needed.
Into the bath are firmly fixed three earthenware or porcelain
dye-pots; steam for heating can be sent through the trunnions. After
the dyeing tests have been made the apparatus can be turned over and
the contents of the dye-pots emptied into a sink which is provided for
the purpose.

Many other pieces of apparatus have been devised and made for the (p. 214)
purpose of carrying on dyeing experiments on the small scale, but it
will not be needful to describe these in detail. After all no more
efficient apparatus can be desired than that described above.

Dyeing experiments can be made with either yarns or pieces of cloth,
swatches as they are commonly called; a very convenient size is a
small skein of yarn or a piece of cloth weighing 5 grammes. These test
skeins or pieces ought to be well washed in hot water before use, so
that they are clean and free from any size or grease. A little soda or
soap will facilitate the cleansing process.

In carrying out a dyeing test the dye-pot should be filled with the
water required, using as little as is consistent with the dye-swatch
being handled comfortably therein, then there is added the required
mordants, chemicals, dyes, etc., according to the character of the
work which is being done.

Of such chemicals as soda, caustic soda, sodium sulphate (Glauber's
salt), tartar, bichromate of potash, it will be found convenient to
prepare stock solutions of known strength, say 50 grammes per litre,
and then by means of a pipette any required quantity can be
conveniently added. The same might be followed in the case of dyes
which are constantly in use, in this case 5 grammes per litre will be
found strong enough.

Supposing it is desired to make a test of a sample of Acid Red, using
the following proportions, 2 per cent. dye-stuff, 3 per cent.
sulphuric acid and 15 per cent. Glauber's salt, and the weight of the
swatch which is being used is 5 grammes, the following calculations
are to be made to give the quantities of the ingredients required:--

For the dye-stuff, 5 (weight of swatch) multiplied by 2 (per cent. of
dye) and divided by 100 equals (5 x 2) / 100 = 0.1 gramme of dye.

For the acid we have similarly (5 x 3) / 100 = 0.15 gramme of (p. 215)

For the Glauber's salt (5 x 15) / 100 = 0.75 gramme of Glauber's salt.

These quantities may be weighed out and added to the dye-bath, or if
solutions are kept a calculation can be made as to the number of cubic
centimetres which contain the above quantities, and these measured out
and added to the dye-bath.

When all is ready the bath is heated up, the swatch put in and the
work of the test entered upon.

Students are recommended to make experiments on such points as:--

The shades obtained by using various proportions of dye-stuffs.

The influence of various assistants: common salt, soda, Glauber's
salt, borax, phosphate of soda in the bath.

The influence of varying proportions of mordants on the shade of

The value of various assistants, tartar, oxalic acid, lactic acid,
sulphuric acid, on the fixation of mordants.

The relative value of tannin matters, etc.

Each dyer should make himself a pattern book into which he should
enter his tests, with full particulars as to how they have been
produced at the side.

It is important that a dyer should be able to make comparative
dye-tests to ascertain the relative strength of any two or more
samples of dyes which may be sent to him.

This is not difficult but requires considerable care in carrying out
the various operations involved.

0.5 gramme of each of the samples of dyes should be weighed out and
dissolved in 100 c.c. of water, care being taken that every (p. 216)
portion of the dye is dissolved before any of the solution is used in
making up the dye-vats. Care should be taken that the skeins of yarn
or swatches of cloth are exactly equal in weight, that the same volume
of water is placed in each of the dye-pots, that the same amounts of
sulphate of soda or other dye assistants are added, that the
quantities of dye-stuffs and solutions used are equal, in fact that in
all respects the conditions of dyeing are exactly the same, such in
fact being the vital conditions in making comparative dye-tests of the
actual dyeing strength of several samples of dyes.

After the swatches have been dyed they are rinsed and then dried, when
the depths of shade dyed on them may be compared one with another. To
prevent any mistakes it is well to mark the swatches with one, two,
three or more cuts as may be required.

It is easier to ascertain if two dyes are different in strength of
colour than to ascertain the relative difference between them. There
are two plans available for this purpose; one is a dyeing test, the
other is a colorimetric test made with the solutions of the dyes.

#Dyeing Test.#--This method of ascertaining the relative value of two
dyes as regards strength of colour is carried out as follows. A
preliminary test will show which sample is stronger than the other;
then there is prepared a series of dye-vats, one contains a swatch
with the deepest of the two dyes, which is taken as the standard, the
others with the other dye but containing 2, 5 and 10 per cent. more
dye-stuff, and all these are dyed together, and after drying a
comparison can be made between these and the standard swatch, and a
judgment formed as to the relative strength of the two dyes; a little
experience will soon enable the dyer to form a correct judgment of the
difference in strength between two samples of dye-stuff.

The colorimetric test is based on the principle that the colour (p. 217)
of a solution of dye-stuff is proportionate to its strength. Two white
glass tubes, equal in diameter, are taken; solutions of the
dye-stuffs, 0.5 gramme in 100 c.c. of water, are prepared, care being
taken that the solution is complete. 5 c.c. of one of these solutions
is taken and placed in one of the glass tubes, and 5 c.c. of the other
solution is placed in the other glass tube, 25 c.c. of water is now
added to each tube and then the colour of the diluted liquids is
compared by looking through in a good light. That sample which gives
the deepest solution is the strongest in colouring power. By diluting
the strongest solution with water until it is of the same depth of
colour as the weakest, it may be assumed that the length of the
columns of liquid in the two tubes is in proportion to the relative
strength of the two samples. Thus if in one tube there are 30
centimetres of liquid and in the other 25 centimetres, then the
relative strength is as 30 to 25, and if the first is taken as the
standard at 100 a proportion sum may be worked out as follows:--

30: 25 :: 100 : 83.3;

that is, the weakest sample has only 83.3 per cent. of the strength of
the strongest sample.

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